Current production strap feed assemblies include a drive wheel and idler wheels that are operated during a four cycle banding process. The cycles include a feed cycle wherein an electric drive motor is driven in a first direction to feed a strap through a track and around the item to be banded. The drive motor rotates a knurled drive wheel with respect to an idler wheel assembly that cooperates with the drive wheel to apply a minimal drive force during the feed cycle. The drive motor is controlled to rotate in an opposite direction during a tension cycle wherein the strap is pulled in a direction opposite to the feed direction outwardly of the track and around the item to cause the strap to tighten the strap around the item to be banded.
During the tension cycle a greater force is applied on the strap by the idler wheel and drive wheel so as to keep the strap from slipping during the tension cycle. Once the tensioning is complete, leading and trailing strap portions are fastened together during a crimping cycle to create a sealed connection around the item to be banded. The strap is then severed during a cutting cycle to separate a sealed strap loop from the trailing portion of the strap material.
Current strap feed assemblies include those shown in U.S. Pat. Nos. 3,566,778 and 3,442,203 in which a two wheel assembly provides a minimal force in the strap feed direction and a greater force on the strap during reverse drive in which the strap is tensioned. In such arrangements, a pull-back force produced during the tension cycle is limited to approximately 80 pounds of force before the strap begins to slip. While suitable for certain applications, the upper force limit is not adequate when the items are made up of material or components which must be compressed during the tension cycle such as heat exchangers with tube bundles.
Other strap feed assemblies include a hydraulic cylinder to move the drive head to perform the tensioning step. Initially, the feed wheels are reversed to pull back on the strap to take up most of the slack in the strap. A hydraulic cylinder is then moved and serrated edges thereon grip the strap and pull it further to set a desired tension level under the control of a pressure sensor and regulator that will control the pressure in the hydraulic cylinder to properly tension the strap.
In each case, the strap feed assemblies of the prior art can deform the trailing end of the strap through guide tracks for banding the item.